The analysis and prediction of the performance of materials upon exposure to radiation, such as ultraviolet radiation, is important for many industrial and commercial applications.
One industrial area where such analysis and prediction is especially important is in the area of photolithography. Photolithographic processes typically involve the use of organic photoresist materials which are patternwise exposed to radiation (most typically some form of ultraviolet radiation. Modern photoresist chemicals typically rely on radiation-induced chemical process that results in emission of volatiles. Such volatiles may cause catastrophic or incremental damage to expensive photolithographic equipment.
It may also be desired to determine the chemical effects of ultraviolet or other radiation exposure in order to obtain information regarding the actual chemical processes occurring in a multi-component chemical system such as a photoresist. Such information may be useful in determining the proper components and proportions to be used in the photoresist formulation.
Unfortunately, photoresist development typically takes place in an ordinary chemical laboratory where access to photolithographic equipment is not possible or impractical (e.g., due to logistics, expense, etc.) or is undesirable (e.g., where equipment damage is a concern). In the laboratory, it is difficult to simulate actual photochemical and catalytic processes that would occur upon radiation exposure in the photolithographic tool. A typical solution to this problem has been to use heating or action of chemical treatments to simulate the reactions that would occur in the photolithographic tool. These methods have not been adequate to reliably predict volatiles evolution.
Thus, there is a need for improved laboratory methods and laboratory scale apparatus for determining the performance of materials upon irradiation.
The invention provides a laboratory scale apparatus for simulation of UV radiation exposure behavior with real time analysis of output volatiles. The invention also provides methods of performing real time analysis of volatile species generated upon UV irradiation of a material sample. The apparatus and methods of the invention are especially useful in the analysis and screening of photoresist materials.
In one aspect, the invention encompasses an apparatus for analysis of volatiles emitted from a material sample upon exposure to radiation, the apparatus comprising:
a) a chamber adapted to hold a material sample, the chamber comprising (i) a window for transmission of radiation to the sample, (ii) a holder for the sample, (iii) an inlet for sweep gas, and (iv) an outlet for volatiles-containing sweep gas,
b) a gas supply means for supplying sweep gas to the chamber,
c) a radiation source for transmitting radiation to the sample through the window, and
d) a volatiles analyzing means adapted to receive and analyze volatiles-containing gas passing from the chamber through the outlet upon exposure of the sample to radiation from the radiation source.
In another aspect, the invention encompasses a method of determining the composition of volatiles emitted from a material upon exposure to UV radiation, the method comprising:
a) placing the material on a substrate,
b) placing the substrate in a chamber adapted to hold the substrate, the chamber comprising (i) a window for transmission of radiation to the substrate, (ii) an inlet for sweep gas, and (iv) an outlet for volatiles-containing sweep gas,
c) supplying sweep gas to the chamber,
d) irradiating the substrate by transmitting radiation through the window, thereby causing evolution of volatiles from the material, the volatiles being entrained in the sweep gas,
e) analyzing the volatiles-containing sweep gas using spectroscopy, the analysis being conducted as the volatiles are being formed during the irradiation.
The apparatus and methods of the invention are especially useful for the analysis of photoresist materials. A preferred analysis is mass spectroscopy or Fourier Transform Infrared Spectroscopy (FTIR). The irradiation is preferably performed with an ultraviolet radiation source capable of producing radiation at wavelengths of about 400 nm or less.
These and other aspects of the invention are described in further detail below.